sshdump: remove redundant ssh_userauth_agent call

sshdump: remove redundant ssh_userauth_agent call

Since the original introduction of sshdump, ssh_userauth_publickey_auto
was already in use which would try the ssh-agent on non-Windows
platforms. There is no need to explicitly call ssh_userauth_agent which
is dead code anyway due to a typo in the macro name.

Change-Id: I976ec3da9e35ade63983ba5ca01163714d466912
Reviewed-on: https://code.wireshark.org/review/37476
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Dario Lombardo <lomato@gmail.com>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>